This invention relates to silica powders and mixed silica-oxide powders and methods of preparing such powders for use as catalyst supports for polymerization processes.
The use of amorphous gels and precipitates as support material for polymerization catalysts is known. For example, aluminophosphate gels and precipitates have often been used for such support materials. In some cases, the support was improved by incorporating silica into the aluminum phosphate support.
While aluminophosphates have long been known, along with their methods of preparation, such aluminophosphates have not as yet achieved commercial success. Part of this is believed to be that the prior art aluminophosphates lacked a combination of physical properties which have been found to characterize superior polymerization catalysts. It is the combination of a high macropore volume of at least 0.1 cc""s per gram plus a fragmentation potential (to be defined below) of preferably 30 to 60 plus a preferred mesopore volume of 0.3 to 0.8 cc""s per gram which particularly characterize the superior polymerization catalysts. In two prior inventions of Applicants (Pecoraro and Chan, U.S. patent application Ser. No. 08/742,794 U.S. Pat. No. 6,022,313; Auburn and Pecoraro, U.S. patent application Ser. No. 08/741,595 U.S. Pat. No. 5,869,587), which are incorporated herein by reference, a new aluminophosphate with both high macropore volume and a fragmentation potential about 30 was developed which was also both physically and thermally stable. It is believed that the presence of sheets of aluminophosphate in the microstructure results in the packing of the microstructures in such a way that a high macropore volume and a high fragmentation potential are achieved along with physical and thermal stability.
In another related invention by Applicants (U.S. application Ser. No. 08/961,825 U.S. Pat. No. 6,111,037, Auburn, Pecoraro and Chan), which is a continuation-in-part of Ser. Nos. 08/741,595 and 08/742,794 discussed above, and which is also incorporated by reference herein, a silica-modified, amorphous aluminophosphate composition which like the previous inventions exhibits a microstructure of sheets and exhibits spheres of silica-modified aluminophosphate as well.
The use of silica alone or the combination of silica with other oxides such as alumina or titania or vanadia to form such amorphous compositions for use as polymerization catalyst support material is also known. Previously, the microstructure of such supports primarily contained small particles. As a result of this small particle structure, it was difficult to tailor the materials over a wide range of pore sizes, distributions and volumes, and of acceptable fragmentation characteristics.
It would be desirable to find silica support materials which could be used over a wide range of pore sizes, distributions and volumes and of acceptable fragmentation characteristics.
The present invention has achieved such materials. The present invention has achieved high surface area, amorphous silicas which surprisingly form a continuous network matrix, rather than the typical small particles found in conventional amorphous silicas. Furthermore, the pore size and the distribution and volume of the pore size can be tailored over a wide range.
Surprisingly, also, the present invention achieves an amorphous SiO2 base composition with a non-particulate, dense, network matrix and encapsulated less dense, non particulate regions with true macropores. In one embodiment, the present invention also comprises a sheet-like microstructure.
One object of the present invention is to provide an amorphous SiO2 or mixed oxide silica base composition comprising:
(a) a non-particulate, dense, continuous network matrix; and
(b) encapsulated, less dense, non particulate regions with true macropores.
Another object of the present invention is to provide such an amorphous SiO2 or mixed oxide silica base composition in which the gel matrix further comprises a sheetlike microstructure.
Still another object of-the present invention is to provide such an amorphous SiO2 or mixed oxide silica base composition in which the composition has surface areas in a range of from 150 to 600 m2/gm.
Yet another object of the present invention is to provide such an amorphous SiO2 or mixed oxide silica base composition in which the composition has a mean mesopore diameter in a range of from 60 to about 250 xc3x85.
An additional object of the present invention is to provide such an amorphous SiO2 or mixed oxide silica base composition in which the composition has a measured pore volume in a range of from about 0.5 to 1.5 cc/gm.
Still another object of the present invention is to provide such an amorphous SiO2 or mixed oxide silica base composition in which the composition has a macropore volume of at most 0.5 cc/gm.
Yet another object of the present invention is to provide an amorphous mixed oxide silica base composition selected from the group consisting of silica alumina, silica titania, silica vanadia and silica zirconia.
An additional object of the present invention is to provide powders produced from such an amorphous SiO2 or mixed oxide silica base composition.
A further object of the present invention is to provide such powders which are spray dried.
Yet a further object of the present invention is to provide such powders which are vacuum dried.
Still a further object of the present invention is to provide such spray dried powders having fragmentation potentials in a range of from about 20 to about 30.
Another object of the present invention is to provide a catalyst comprising such a SiO2 base composition, the composition being impregnated with a catalytic amount of at least one transition metal-containing compound.
Yet another object of the present invention is to provide such a catalyst in which the at least one transition metal-containing compound is a chromium compound.
Still another object of the present invention is to provide such a catalyst in which the at least one transition metal-containing compound is present in an amount of 0.1 weight percent or greater based on the total catalyst weight.
An additional object of the present invention is to provide such a catalyst in which the at least one transition metal-containing compound is present in an amount in the range of from about 0.1 weight percent to about 10 weight percent.
Yet an additional object of the present invention is to provide a polymerization process comprising contacting such a catalyst with at least one alpha-olefin under polymerization conditions.
Still an additional object of the present invention is to provide a method for preparing a silica gel composition which is a precursor material for a silica powder material with a microstructure comprising a non-particulate, dense, continuous network matrix and encapsulated, less dense, non particulate regions with true macropores, the method comprising:
(a) forming a first aqueous solution comprising silica ions;
(b) forming a second aqueous solution capable of neutralizing said first aqueous solution; and
(c) contacting said first and second aqueous solutions in a mixer-reactor under mixing conditions to form the silica gel composition.
An additional object of the present invention is to provide an olefin polymerization catalyst prepared from a silica gel composition obtained by such a method.
Yet another object of the present invention is to provide such a method in which the first aqueous solution is an acidic solution comprising sodium silicate and acid and in which the second aqueous solution has a pH above 8.
Still an object of the present invention is to provide such a method in which the second aqueous solution is an ammonia based material selected from the group consisting of ammonium hydroxide; ammonium carbonate; ammonium bicarbonate and urea.
An additional object of the present invention is to provide such a method in which the first aqueous solution is a basic solution of sodium silicate and in which the second aqueous solution has a pH below 6.
Yet an additional object of the present invention is to provide such a method in which the second aqueous solution is sulfuric acid.
Still an additional object of the present invention is to provide such a method, in which the apparent average shear rate in the mixer-reactor is greater than about 0.5xc3x97104 secxe2x88x921.
Another object of the present invention is to provide such a method in which the neutralization step is conducted in such a manner that the pH of the combined first aqueous solution and the neutralizing medium is controlled in the range of about 3.5 to about 11.
Yet another object of the present invention is to provide such a method in which the catalyst is activated by being heated to a temperature in the range of 300xc2x0 C. to 900xc2x0 C. for from 2 to 16 hours.
Still another object of the present invention is to provide such a method further comprising the steps of:
(a) preparing an aqueous slurry of amorphous silica gel by continuously feeding an acidic solution comprising sodium silicate and acid to an emulsifier mixer while simultaneously and continuously feeding to said mixer an alkaline solution;
(b) operating said mixer with sufficient shear so that the precipitated silicate has sheets of silica in its microstructure;
(c) recovering said silica from said aqueous slurry using a vibrating filtration membrane to a solids content from 8 to 20 wt. %, after washing;
(d) drying and calcining the silica from (c);
(e) dispensing a chromium compound substantially uniformly onto said silica to form a catalyst having from 0.01 to 4 wt. % chromium;
(f) drying said catalyst; and
(g) activating said dry catalyst from (f) by heating to a temperature from 300xc2x0 C. to 900xc2x0 C. for from 2 to 16 hours.
Yet another object of the present invention is to provide an olefin polymerization catalyst prepared by such a method.
Another object of the invention is to provide such a method further comprising aging the silica gel composition in deionized water for up to one hour.
Yet another object of the present invention is to provide a method of preparing the silica powder composition from such a silica gel composition comprising the steps of:
(a) washing the silica gel with solutions of ammonium acetate, bicarbonate or nitrate;
(b) washing the silica gel composition in deionized water to further replace salts-contaminated water in the composition with fresh water; and
(c) drying the washed composition to remove substantially all water.
Still another object of the present invention is to provide such a method further comprising calcining the dried composition in a fixed fluid bed type calciner for up to 8 hours at a maximum temperature of 450xc2x0 C.
Another object of the present invention is to provide a polymerization process comprising contacting at least one mono-1-olefin having from 2 to 8 carbon atoms per molecule under polymerization reaction conditions in a polymerization reaction zone with a catalyst comprising an active catalytic component on a silica support comprising (a) a non-particulate, dense, gel matrix; and (b) encapsulated regions with true macropores.
Still another object of the present invention is to provide such a polymerization process in which the catalytic component comprises a chromium component on the silica support.
Yet another object of the present invention is to provide such a polymerization process in which the at least one mono-1-olefin is selected from ethylene; propylene; butene-1; hexene-1 and octene-1.
An additional object of the present invention is to provide such a polymerization process in which the at least one mono-1-olefin comprises ethylene and from 0.5 to 2 mole percent of one additional mono-1-olefin selected from propylene; butene-1, hexene-1 and octene-1.
A further object of the present invention is to provide a method for preparing silica alumina powder material with a microstructure comprising a non-particulate, dense, continuous network matrix and encapsulated regions with true macropores and sheets, the method comprising:
(a) preparing an acid aqueous solution comprising aluminum and silicon ions;
(b) preparing a basic aqueous solution comprising ammonium hydroxide;
(c) mixing the acidic aqueous solution and the basic aqueous solution in a mixer to obtain a gel slurry with a microstructure comprising a non-particulate, dense, continuous network matrix, encapsulated regions with true macropores and sheets;
(d) maintaining the gel at approximately pH 8.0 for up to one hour before washing the gel slurry;
(e) washing the gel slurry first with an aqueous ammonium acetate or ammonium bicarbonate solution, then with water to obtain a gel conductivity below 1,000 mmhos;
(f) acidifying and concentrating the gel slurry by adding acid to the gel slurry to achieve a pH below 6.0 while gradually removing water from the gel slurry; and
(g) drying and calcining the gel slurry to form the silica-alumina powder material.